Generating PDFs for Invoices and Reports

If you are building a B2B agent, eventually you will hit the "Paper Ceiling."

Your agent can negotiate a deal, schedule a meeting, and answer support questions. But when the client says, "Great, send me an invoice," the agent hits a wall. It can send text. It can send Markdown. But it cannot send a PDF.

And in the business world, if it's not a PDF, it's not real.

The Problem: The Format Gap

LLMs produce streams of tokens (text). They do not produce binary files. They cannot layout a page, handle page breaks, or embed fonts.

To cross the Paper Ceiling, we need a translator. We need a tool that takes the LLM's structured data (JSON) and paints it onto a canvas (PDF).

The Solution: HTML as the Intermediate Language

The easiest way to generate a PDF is to generate HTML first. LLMs are excellent at writing HTML. We can use a service (like PDFShift, DocRaptor, or a headless Chrome wrapper) to convert that HTML into a PDF.

The Implementation

We will build a tool called generate_invoice_pdf.

/**
 * Generates a PDF invoice URL.
 * 
 * Description for LLM: "Create a PDF invoice for a client based on a list of items."
 */

// 1. Structured Input
// We don't ask the LLM to write the HTML directly in the input arguments
// because it might hallucinate broken tags.
// Instead, we ask for DATA. We will wrap the data in HTML ourselves.
type InvoiceItem = {
  description: string;
  amount: number;
};

type Input = {
  clientName: string;
  invoiceNumber: string;
  items: InvoiceItem[];
};

export default async function generateInvoice(args: Input) {
  const apiKey = Deno.env.get("PDF_API_KEY");
  if (!apiKey) throw new Error("Missing PDF_API_KEY");
  
  const { clientName, items, invoiceNumber } = args;
  
  // 2. The Logic Layer
  // We calculate totals here. Why? Because LLMs are bad at math (see our other article).
  // We trust the LLM to list the items, but we do the summing.
  const total = items.reduce((sum, item) => sum + item.amount, 0);

  // 3. The Templating
  // We inject the data into a clean, professional HTML template.
  // This ensures every invoice looks on-brand, no matter what the AI does.
  const html = `
    <html>
      <body style="font-family: sans-serif; padding: 40px;">
        <h1 style="color: #333;">Invoice #${invoiceNumber}</h1>
        <p><strong>Bill To:</strong> ${clientName}</p>
        <table style="width: 100%; border-collapse: collapse; margin-top: 20px;">
          <tr style="background: #eee;">
            <th style="padding: 10px; text-align: left;">Item</th>
            <th style="padding: 10px; text-align: right;">Cost</th>
          </tr>
          ${items.map(i => `
            <tr>
              <td style="padding: 10px; border-bottom: 1px solid #ddd;">${i.description}</td>
              <td style="padding: 10px; border-bottom: 1px solid #ddd; text-align: right;">$${i.amount.toFixed(2)}</td>
            </tr>
          `).join("")}
        </table>
        <h2 style="text-align: right; margin-top: 20px;">Total: $${total.toFixed(2)}</h2>
      </body>
    </html>
  `;

  // 4. The Conversion
  // We send the HTML to our PDF service.
  const res = await fetch("https://api.pdfservice.com/convert", {
    method: "POST",
    headers: { 
      "Authorization": `Basic ${apiKey}`,
      "Content-Type": "application/json"
    },
    body: JSON.stringify({ source: html })
  });

  const data = await res.json();

  // 5. The Handoff
  // We return a URL. The agent can now say:
  // "Here is your invoice: [Link]"
  return { 
    success: true, 
    pdfUrl: data.url, 
    expiresIn: "24h"
  };
}

The Execution Story

User: "Send an invoice to Acme for the 'Q1 Strategy Session'. It was $5,000."

Agent Action:

Recognizes the intent: generate_invoice.
Generates an invoice number (e.g., "INV-2024-001").

Calls the tool:

{
  "clientName": "Acme Corp",
  "invoiceNumber": "INV-2024-001",
  "items": [
    { "description": "Q1 Strategy Session", "amount": 5000 }
  ]
}

The tool calculates the total, builds the HTML, converts it, and returns https://files.dwizi.com/inv-2024-001.pdf.

Agent Response: "I've generated the invoice for Acme. You can download it here: [Link]. Should I email it to them?"

Now the agent isn't just chatting about work. It's doing the paperwork.

Generating PDFs for Invoices and Reports

Generating PDFs for Invoices and Reports

The Problem: The Format Gap

The Solution: HTML as the Intermediate Language

The Implementation

The Execution Story

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